1. Field of the Invention
The present invention relates to a linear driving apparatus which can be utilized for example for a copying machine, a printer, a magnetic disk apparatus.
2. Description of the Prior Art
FIG. 1a is a schematic drawing of a conventional linear driving apparatus.
In the drawing, the base frame 74 there are provided a movable member 71 on which a moving unit 72 of a magnetic field forming member 73 which are the major components of the linear driving apparatus. The movable member 71 is freely movably disposed on a base frame 74 in the direction of arrow mark F as illustrated in the drawing by a guide shaft (not illustrated). On the other hand, the magnetic field forming member 73 is fixed onto the base frame 74.
When a prescribed exciting current is supplied to coils of the magnetic field forming member 73 under a state where the magnetic fluxes from the magnetic field forming member 73 are crossed, a steering force F is exerted on the moving unit 72 and the movable member 71. Through regulation of the exciting current, the position setting control for the object to be moved (not illustrated) which is connected to the movable member 71 is realized.
However, according to the prior art device as above, the following defects occur.
When an exciting current is supplied to the movable member 71 and a steering force F is exerted, a reaction force Fr (Fr=-F) works on the magnetic field forming member 73 as a counter-effect of the steering force F, which is transmitted to the base frame 74, thereby causing undesirable results such as vibration or deformation of the base frame 74.
The above defect provides a particularly significant problem in the case where the linear driving apparatus is applied to the copying machine or magnetic disk apparatus.
For examples, in the magnetic disk apparatus, data errors occur, while in the high speed copying machine an original document is displaced or the copying machine per se is displaced from the setting position.
FIG. 1c shows another example of the linear driving apparatus which is used for a wafer exposure X-Y stage which is required an accurate positioning control. In the example, the linear driving apparatus is provided on a vibration preventing table 1" which is situated on a floor 5" through vibration absorbing members 4".
In the arrangement mentioned above, the same problem as mentioned in the apparatus shown in FIG. 1a occurs. In addition, with the movement of an object driven by the linear driving apparatus, the vibration preventing table 1" is slanted by the change of the gravity center of the vibration preventing table 1".
FIG. 1b is a further example of a conventional linear driving apparatus used in a copying machine in which a RDH 40' (recirculating document handler drum) is provided on the base frame 70 which winds an original document 60' from Da to Db direction. An original plat form 50' is disposed above the copying machine. A guide 720 for linearly moving an original reader 730 made of CCD for reading the original is provided below the RDH drum 40' and the original platform 50'. In order to move the original reader 730, a linear motor 710 which is similar to the linear driving apparatus mentioned above is used. In FIG. 1b, 711 denotes the magnetic field forming member, 712 denotes the moving unit. By the steering force acting on the moving unit 712, the original reader 730 is linearly moved along the guide 720.
In order to copy the original 60' by winding on the RDH drum 40', the content of the original is read by the original reader 730 situated at the position Dc. In making a copy, the original reader 730 is moved to the position Dd by driving the linear motor and by scanning the original again to the De, the original is read.
In the conventional copying machine as mentioned above, the distance of moving the original reader is relatively long, and the moving unit 711 of the linear motor 710 must be long, whereby the above problem becomes an obstacle to reduce the cost of the copying machine. expensive